It maintains six-days-a-week service to 150 million locations, operates 26,410 post offices, and handled nearly 150 billion pieces of mail in 2017 — or 47 percent of all the mail in the world. UPS and FedEx could not possibly handle that volume, especially not to unprofitable far-flung locations — not even for parcels, as the USPS accounts for about 40 percent of Amazon shipping.